Reverberatory furnace practice



y 17, 1956 c. G. DE LAVAL, JR 2,755,180

REVERBERATORY FURNACE PRACTICE Filed March 15, 1952 INVENTOR United States Patent REVERBERATORY FURNACE PRACTICE Carl George de Laval, Jr., Mount Lebanon Township, Allegheny County, Pa.

Application March 15, 1952, Serial No. 276,744

12 Claims. (Cl. 75-43) This invention relates to reverberatory furnace practice and particularly to a method of operating a direct fired reverberatory furnace for the manufacture of iron castings (both gray iron and malleable iron). Direct fired reverberatory furnaces have been used to a large extent in the nonferrous metal casting industry. They have, however, not been completely satisfactory for use in iron foundry practice although they have many characteristics Which would make them desirable there. Direct fired reverberatory furnaces heat rapidly, attain high temperatures and are easily charged and cast from, all of which are desirable in iron foundry practice. However, it has been impossible heretofore to take advantage of these characteristics and particularly of the very desirable high temperatures which can be attained because the linings ordinarily used erode too rapidly for practical use. Silica brick linings are unsatisfactory because they melt and are thereby destroyed at the desirable higher temperatures. It is likewise impractical to use a basic lining in such furnaces with any degree of satisfaction because of the large amounts of sand which enter the furnace with usual foundry sprue. In the customary iron foundry practice using reclaimed foundry sprue approximately two inches of the thickness of the basic lining has been lost with each consecutive heat making them economically unsuitable for use in such practice. Alumina-silica brick will withstand the high temperatures present in the reverberatory furnace but are eroded away rapidly by all of the practices ordinarily used in the production of foundry iron. Direct fired reverberatory furnaces have accordingly found slight use in the iron casting field and particularly in high temperature castings where the internal refractory temperature approaches 3000 F. and metal taphole temperature is 2800 F.

I have discovered a method of operating direct fired reverberatory furnaces which permits their use for the manufacture of iron castings without excessive erosion of the lining even at high casting temperatures. I have found that by following the steps of lining the furnace with an alumina-silica lining, adding a proper reducing agent to the charge in the stack of the furnace and along with the cold metal charge, maintaining a slag which is substantially insoluble in mineral acids above the molten metal after the melt-down and periodically adding a sufficient amount of reducing agent to substantially prevent the activation and/ or subsequent formation of FeO during the heating period I am able to produce foundry iron in a direct fired reverberatory furnace without seriously eroding the walls of the furnace or otherwise detrimentally affecting the refractory lining. I have found that the furnace lining should contain not less than about 50% alumina, that the most suitable reducing agents to be added to the metal before the melt-down are calcium carbide, silicon carbide and ferroalloys of silicon preferably those containing 75% or more of silicon. I have found that the slag is best maintained at a V ratio (CaO/SiOz) of 1:2 or less and that preferably the ratio ice 2 of total basic and semibasic components (CaO, FeO, and A1203) to SiOa does not exceed 1:1.

In the accompanying drawing 1 have illustrated a typical direct fired reverberatory furnace having a furnace framework 10 tiltably mounted on a base 11 for ease of pouring. Within the furnace framework is constructed a furnace hearth 12 with sloping sidewalls. At one end of the furnace is provided a charging opening 13 and at the opposite end of the furnace is provided a series of burners 14 directed towards the center of the hearth. Combustion air is carried to the burners 14 through a flexible pipe 15 and manifold 16 from a combustion air blower 17. The fuel (gas or oil) is introduced into the burners by means of a fuel line and regulator, not shown. The hearth 12 is lined with an alumina-silica composition preferably containing not less than about 50% alumina.

The sidewalls of the furnace as well as the charging opening are lined with alumina-silica bricks preferably containing at least about 50% alumina. In the practice of my invention the foundry sprue and scrap and other material to be melted down into foundry iron are charged into the charging opening 13 along with suflicient reducing agent, either calcium carbide, silicon carbide or ferrosilicon, to substantially prevent the formation of FeO in the iron during the melt-down period. By substantially prevent I do not mean that the FeO is entirely prevented but that it will not exceed about 15% of the slag. As soon as the scrap charge has melted down and a slag is formed the composition of the slag may be adjusted so as to make it substantially insoluble in mineral acids, i. c. has a V ratio less than about 1:2. As the heating of the molten iron progresses the FeO content of the slag is controlled by the addition of one of the reducing agents, calcium carbide, silicon carbide or ferrosilicon, so as to maintain it below 15%. The advantages of reverberatory furnace practice according to my invention are readily apparent from the following examples:

EXAMPLE I Twelve heats were made according to the practice of my invention. in each of these heats the slag was maintained at a V ratio of 1:2-|- and was acid insoluble. Typical of the analysis of the slags of this series are those from representative heats of the series given in Table 1 below.

Table 1 Heat Number CaO SiOz FeO A130,

Each of these slags was acid insoluble. An inspection of the furnace after these heats were completed showed a maximum surface loss from the lining of approximately inch.

EXAMPLE II A series of thirteen heats was made in which the V ratio of the slag was increased above the 1:2 maximum ratio of my process. Typical of the slags resulting from these heats are those from the first two heats of the series given in Table 2 below.

The inspection of the furnace after these heats were completed showed a furnace loss of brick at the slag line of approximately 1 inches.

EXAMPLE III A series of ten heats was made in which no reducing agent was added to the charge and no lime addition made. The slags typical of this series are illustrated by the slags from the first two heats of the series given in Table 3 below.

Inspection of the furnace after these heats were completed showed a surface loss of brick at the slag line of 2 inches.

Comparison of the above examples shows that the furnace lining was eroded less than A inch by ten heats in which my practice was followed whereas in the ordinary practices where the V ratio of the slag was not controlled within my limits and the reducing agent was not added to the charge at the melt-down, the loss of brick at the slag line amounted to from 1 /2 inches to 2 /2 inches, an average of eight times greater loss. Prior to my invention it has been impossible to get more than approximately ten heats out of a direct fired reverberatory furnace without relining it when operating at high taphole temperatures (temperatures in the region of 2800 F.). By using the process of my invention I am able to increase the number of such heats to approximately one hundred before it becomes necessary to reline the furnace. Using a lower taphole temperature the number of heats by the ordinary practice is approximately forty whereas according to my practice the number of heats possible is increased to several hundred.

While I have illustrated and described a present preferred practice of my invention it will be understood that it may be otherwise embodied within the scope of the following claims.

I claim:

1. The method of operating a direct fired reverberatory furnace for the manufacture of iron castings comprising the steps of lining the furnace with an alumina-slicia lining having not less than 50% alumina, adding to the furnace with the charge a sutficient amount of reducing agent to substantially prevent the formation of FeO during the melt-down, maintaining a substantially acid insoluble slag over the molten metal during the heating period, and adding suflicient reducing agent during the heatingperiod to substantially prevent the formation of FeO from the molten metal.

2. The method of operating a direct fired reverberatory furnace comprising the steps of lining the furnace with an alumina-silica lining having not less than 50% alumina, adding a reducing agent of the group calcium carbide, silicon carbide and ferrosilicon to the charge in an amount to substantially prevent the formation of FeO during the melt-down, maintaining a substantially acid insoluble slag over the molten iron during the heating period, and adding a reducin agent of the group calcium carbide, silicon carbide and ferrosilicon to the bath during the heating period in sufficient amount to substantially prevent the formation of FeO from the molten metal.

3. The method of operating a direct fired reverberatory furnace for the production of'foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing at least 50% alumina, adding to the furnace with the charge a suflicient amount of reducing agent to substantially prevent the formation of FeO from the charge during the melt-down, maintaining the V ratio. of

the slag below 1:2 during the heating period, and adding a reducing agent to the bath during the heating period in amounts sufficient to prevent the formation of FeO from the molten metal.

4. The method of operating a direct fired reverberatory furnace for the production of foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing not less than 50% alumina, adding a reducing agent of the group calcium carbide, silicon carbide and ferrosilicon with the charge in an amount sufficient to substantially prevent formation of FeO during the melt-down, maintaining the slag at a V ratio below 1:2 during the heating period, and adding a reducing agent of the group calcium carbide, silicon carbide and ferrosilicon to the molten bath during the heating period in an amount sufficient to substantially prevent an increase in the FeO concentration above that present in the melt-down.

5. The method of operating a direct fired reverberatory furnace for the production of foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing not less than 50% alumina, adding a sufiicient amount of calcium carbide to substantially prevent the formation of FeO during the melt-down, maintaining the slag at a V ratio below 1:2 during the heating period, and adding a sufiicient amount of calcium carbide to substantially prevent an increase in the FeO concentration during the heating period above that present in the meltdown.

6. The method of operating a direct fired reverberatory furnace for the production of foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing not less than 50% alumina, adding a sufi'icient amount of silicon carbide to substantially prevent the formation of FeO during the melt-down, maintaining the slag at a V ratio below 1:2 during the heating period, and adding a sufiicient amount of silicon carbide to substantially prevent an increase in the R30 concentration during the heating period above that present in the melt-down.

7. The method of operating a direct fired reverberatory furnace for the production of foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing not less than 50% alumina, adding a sutficient amount of ferrosilicon to substantially prevent the formation of FeO during the melt-down, maintaining the slag at a V ratio below 1:2 during the heating period, and adding a suflicient amount of ferrosilicon to substantially prevent an increase in the FeO cocncentration during the heating period above that present in the melt-down.

8 A method of operating a direct fired reverberatory furnace for the production of foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing not less than 50% alumina, adding a reducing agent of the group calcium carbide, silicon carbide and ferrosilicon with the charge in an amount sufficient to prevent the formation of more than about 15% FeO during the melt-down, maintaining the slag at a V ratio below, 122 during the heating period, and adding a reducing agent of the group calcium carbide, silicon carbide and ferrosilicon to the molten bath during the heating period in an amount sufficient to substantially prevent an increase in the FeO concentration above that present in the melt-down.

9. Amethod of operating a direct fired reverberatory furnace for the production of foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing not less than 50% alumina, adding a sufilcient amount of calcium carbide to prevent the formation of FeO in excess of 15% on the slag during the melt-down, maintaining the slag at a V ratio below 1:2 during the heating period, and adding a sufiicient amount of calcium carbide. to the molten bath during the heating period to substantially prevent an increase in the Pet) concentration above that present in the melt-down.

10. A method of operating a direct fired reverberatory furnace for the. production of foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing not less than 50% alumina, adding a suflicient amount of silicon carbide to prevent the formation of FeO in excess of 15% on the slag during the meltdown, maintaining the slag at a V ratio below 1:2 during the heating period, and adding a sulficient amount of silicon carbide to the molten bath during the heating period to substantially prevent an increase in the FeO concentration above that present in the melt-down.

11. A method of operating a direct fired reverberatory furnace for the production of foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing not less than 50% alumina, adding a sufiicient amount of ferrosilicon to prevent the formation of FeO in excess of 15% on the slag during the melt-down, maintaining the slag at a V ratio below 1:2 during the heating period, and adding a sufficient amount of ferrosilicon to the molten bath during the heating period to substantially prevent an increase in the FeO concentration above that present in the melt-down.

12. A method of operating a direct fired reverberatory furnace for the production of foundry iron comprising the steps of lining the furnace with an alumina-silica lining containing not less than 50% alumina, adding a reducing agent of the group calcium carbide, silicon carbide and ferrosilicon with the charge in an amount sufficient to prevent the formation of more than about 15 FeO during the melt-down, maintaining the slag at a V ratio below 1:2 during the heating period, and adding a reducing agent of the group calcium carbide, silicon carbide and ferrosilicon to the molten bath during the heating period in an amount sufilcient to substantially prevent the FeO concentration in the slag from exceeding about 15%.

References Cited in the file of this patent UNITED STATES PATENTS 566,026 Sweitzer Aug. 18, 1896 585,036 Hunt June 22, 1897 775,887 Berger Nov. 22, 1904 1,089,410 Hethey Mar. 10, 1914 1,326,861 Hadfield Dec. 30, 1919 1,453,468 Kraus May 1, 1923 1,666,312 Runyan Apr. 17, 1928 2,002,010 Hilliard May 21, 1935 2,470,728 Sklenar May 17, 1949 FOREIGN PATENTS 7,599 Great Britain of 1905 

1. THE METHOD OF OPERATING A DIRECT FIRED REVERBERATORY FURNACE FOR THE MANUFACTURE OF IRON CASTINGS COMPRISING THE STEPS OF LINING THE FURNACE WITH AN ALUMINA-SLICIA LINING HAVING NOT LESS THAN 20% ALUMINA, ADDING TO THE FURNACE WITH THE CHARGE A SUFFICIENT AMOUNT OF REDUCING AGENT TO SUBSTANTIALLY PREVENT THE FORMATION OF FEO DURING THE MELT-DOWN, MAINTAINING A SUBSTANTIALLY ACID INSOLUBLE SLAG OVER THE MOLTEN METAL DURING THE HEATING PERIOD, AND ADDING SUFFICIENT REDUCING AGENT DURING THE HEATING PERIOD TO SUBSTANTIALLY PREVENT THE FORMATION OF FEO FROM THE MOLTEN METAL. 